This invention relates generally to hollow components for gas turbine engines and more particularly to hollow airfoils constructed by friction stir welding.
Aluminum forgings in various alloy compositions are commonly used for gas turbine engine components, for example non-rotating airfoils in the fan and compressor. Such airfoils often have a hollow cross-section to minimize their weight. The alloys of choice, e.g. most 2000- and 7000-series aluminum alloys, may be difficult or impossible to join by conventional fusion welding techniques.
Therefore, prior art methods for producing hollow airfoils involve gun drilling to remove core material, or pocket milling followed by adhesive bonding of a cover sheet over the milled pocket. The pocket may or may not be filled with honeycomb material, and may or may not incorporate stiffener ribs for improved load carrying capabilities and/or fatigue resistance.
Gun drilling is a tedious and inefficient method for removing the maximum core material to optimize weight reduction. On the other hand, pocket milling followed by adhesive bonding of a cover has the disadvantage of excessive adhesive bond quality variability, tedious preparation and processing for adhesive bonding success, excessive lap joint widths to obtain adequate adhesive bond strength, and inability to reliably seal the internal pocket from the external environment resulting in excessive susceptibility to undetected internal corrosion and/or stress corrosion cracking over time.
Accordingly, there is a need for an efficient method for producing sealed hollow components with reliable bond quality.